Lychee nutrition: A review

Scientia Horticulturae, 31 (1987) 195-224 195 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

Lychee Nutrition: A Review

C.M. MENZEL and D.R. SIMPSON

Maroochy Horticultural Research Station, Queensland Department of Primary Industries, P.O. Box 5083, Sunshine Coast Mail Centre, Nambour, Qld. 4560 (Australia)

(Accepted for publication 6 November 1986 )

ABSTRACT

Menzel, C.M. and Simpson, D.R., 1987. Lychee nutrition: a review. Scientia Hortic., 31: 195-224.

One of the major factors limiting fruit production in lychee (Litchi chinensis Sonn.) is lack of a suitable nutrition program. Yields may be low because of excessive vegetative growth in winter following late or heavy N fertilization. Deficiencies of N and K, and to a lesser extent of B, Zn and Cu, may limit yield by restricting the set and subsequent development of fruit. There is the pos- sibility that soil features (pH, drainage or salinity) may impair tree health and hence indirectly reduce fruit production.

Priority areas for nutrition research should include: the relationship between vegetative flushing and leaf N; the timing of fertilizer N application during flowering and fruit set; refinement of leaf and soil sampling; the possible role of K in winter dormancy; leaf symptoms of micronutrient deficiencies; and roles of Zn, B and Cu in fruit set.

Keywords:fertilizer;growth;leafanalysis;Litchi chinensisSonn.;lychee; nutrition; soil analysis; yield.

INTRODUCTION

The lychee (litchi), native to southern China, is adapted to the warm sub- tropics, cropping best in regions with brief cool dry frost-free winters and long hot summers with high rainfall and humidity (Menzel, 1983, 1984a). The Chinese recognized the extreme difficulty of maintaining the yield of highly- prized cultivars under climatic, soil or cultural conditions other than those of the trees' original area of selection. According to Groff (1943), however, the lychee is less sensitive to edaphic than to climatic factors. Nevertheless, the whole question of soil type and fertilization in China is confusing, and this is often reflected in low yields (Chapman, 1984a).

Lychee has spread to most of the tropical and subtropical world (Goto, 1960) and commercial industries have developed in several countries (Taiwan, Thai- land, India, South Africa and Australia). Many of the cultivars grown in these

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countries are irregular bearers. Even if flushing is controlled, yields may be low because of poor fruit set, fruit retention or fruit development (Menzel, 1984a). No universal nutrition program seems to be available for lychee, and poor nutrition is likely to be one of the major factors contributing to fluctuating yields. Much research is required before we use nutrition management to manipulate the growth and fruiting cycle of lychee and maintain tree health, tree size and fruit quality.

All plant nutrient concentrations in this review are expressed as mg or pg per g dry weight. All soil nutrients are expressed as mg per kg oven-dry weight, except organic C, which is expressed on a percent dry weight basis.

SOIL TYPE

Lychees are adapted to most soils and will grow and crop successfully in a range of soil types, including alluvial sands, loams, heavy clays, organic soils, calcareous soils (with 30% lime) and rock piles ( Higgins, 1917; Popenoe, 1927; Cobin, 1954; Chandler, 1958; Dickinson, 1962; Singh and Jawanda, 1962; Nijjar, 1972; Kanwar and Nijjar, 1975; Anon., 1978, 1981; Cull and Paxton, 1983; Chapman, 1984b).

In China, the best lychee trees are found in Guangdong Province, close to the rivers, on alluvial sands with good drainage and access to the water table ( Chapman, 1984a). They are also grown in terraces 1.5-2.0 m wide in gravelly sandy loam to loam soils and in swampy areas bisected by canals where the soil has been built up in levees about 0.5-1.0 m above high tide. The soils in Fujian Province are very high in clay, poorly drained and acid in reaction (Winks et al., 1983). When trees are grown in terraces, the planting site is filled with quality loam and organic matter to improve the soil.

Lychees can withstand up to 14 days of immersion, provided the water does not become stagnant, but will die after prolonged immersion (Groff, 1943; Cobin, 1954; Joubert, 1970; Nijjar, 1972; Storey, 1973 ). Trees subjected to continued flooding in China are dwarfed in comparison to those on better-drained soils (Cobin, 1954 ). In southern Queensland, hilling of the soil along the rows to give ridges about 0.5 m high is recommended in wet sites ( Cull and Paxton, 1983), while the addition of drainage pipes is practised in Taiwan (Chang, 1961; Anon., 1981).

Experience in southern Queensland has shown that soils of low water-hold- ing capacity and low fertility make it easier to stress the trees for water and nutrients, and hence reduce tree vigour for cropping (Cull and Paxton, 1983; Chapman, 1984b). This is especially true for early vigorous cultivars (e.g. 'Tai So') grown along the coastal lowlands or sub-coastal mountains. Conse- quently, light-textured sandy and red loams are preferred. Caution needs to be exercised when irrigating trees on these soils during the period of fruiting, so that they do not suffer any stress. Poor drainage in heavy clay soils in southern

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Queensland also increased the incidence of collar rot and root diseases such as ArmiUariella.

Nel (1983) reported that a tremendous network of roots was observed in 'Tai So' (known locally as 'H.L.H. Mauritius' and 'Da Zao' in China) lychee down to a depth of 100 cm in sandy soils in the cooler subtropical areas of South Africa. In contrast, trees growing in clay soils had a shallow root distribution. C.M. Menzel and A.G. Banks (unpublished data, 1984) noted that most of the roots of an 8-year-old 'Tai So' tree growing in a sandy clay loam overlying a heavy clay in subtropical Queensland were in the top 30-40 cm. More recent studies with the same cultivar at a range of sites (Menzel et al., 1986b) showed that soil type influenced total root density and feeder root distribution (depth of soil profile where 80% of roots are located). Sandy soils had more roots in the profile compared to clay soils, but a smaller proportion were found at depth ( feeder root distribution of 0-20 to 0-60 cm, respectively). About 90% of the roots were less than 2 mm in diameter. Site and profile depth had no significant effect on root size distribution.

Howard (1925) showed that although some lychee (cultivar unspecified) roots were found at great depths (3.74 m) in a deep calcareous sandy loam soil in India, most roots were located in the top 45 cm. The deep root system was capable of absorbing enough water from the water table during the dry season to support a large crop. Maximum root growth was observed prior to flowering and after harvest. Howard also demonstrated that maintaining a grass-covered sward along the row had a detrimental effect on both root and shoot growth in lychee trees, presumably because of competition for water and nutrients. Trees were not fertilized during the experiment.

SOIL pH

Hayes (1945) concluded that the lychee is probably capable of growing well on either acid or alkaline soils, but there is little or no critical information on the opt imum soil pH.

Nanz (1955) surveyed the growth and yield of lychee in 11 orchards in Flor- ida. Better performance (not defined) was achieved in the range pH 5.0-5.5. Trees growing in soils where the pH was below 5.0 made poor growth. There were few orchards with a pH greater than 6.1, and the best growth was made in an orchard with a pH of 7.4. Lynch (cited in Nanz, 1955) noted good growth in orchards with a pH of 7.5-7.8. Similarly in India, lychees grew satisfactorily in alkaline soils with up to 30% free lime ( Nijjar, 1972 ).

The pH of lychee soils in China is usually about 5.5 (Groff, 1921). Most soils are naturally acid or acidified by the addition of liquid fertilizer. Nanz (1955) suggested mulching with straw for maintaining a neutral-to-acid pH in Florida.

Rates of lime application in southern Queensland, to bring the soil to a pH

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of 6.0, ranged from 1.0 t ha -1 on a sandy soil with a pH of 5.0 to 7.5 t ha -1 in a clay loam with a pH of 4.5 (Anon., 1984a). It was suggested that no more than 5 t ha- ~ should be applied in any one application on sandy soils. Where more lime was required, a second amount was applied 3 months later.

The poor growth of lychee under alkaline pH has been attributed to micronutrient toxicity/deficiency or lack of mycorrhiza ( Young, 1954; Knight, 1980), but no experimental evidence is available. Aluminium, Mn, Zn and Cu toxicity, and Fe deficiency, have been implicated in plant responses to acid and alkaline conditions, respectively, and need to be considered in lychee. The percentage of cation exchange capacity taken up by A1 (compared to K, Ca, Mg and Na) is considered more important than the pH of the soil itself (Foy, 1983; Haynes, 1984) and has been suggested in other crops to calculate the lime requirement (Black, 1968). This calculates the amount of Ca required to overcome the deleterious effects of both H and A1 ions in the soil solution. Values of A1 saturation calculated for lychee soils in subtropical Queensland ranged from 0.3 to 53.9%. Yields in a range of crops were reduced when A1 saturation exceeded 4%, while others were not affected until it reached 70% or more (Haynes, 1984). Solution-culture experiments have shown that plant growth is little affected by pH within the range 4-8 (Arnon and Johnson, 1942). Although exchangeable A1 has been suggested as a measure of lime requirement, lime rates equivalent to 1.5-3 times the exchangeable Al are usually required to neutralize all the A1 in acid soils ( McLean, 1976; Haynes, 1984). Such results indicate that there are forms of reactive A1 in soils that are not exchangeable with 1 N KC1, but that react with lime. As yet, there is no standard extractant for reactive Al that will give a good estimate of the lime requirement.

SALINITY

There is little information about the response of lychee to excess salts. Lychee appears to be less sensitive than avocado or macadamia (Whiley and Saranah, 1980), but is still in the low-tolerance class of plants (Dahiya et al., 1983; Anon., 1984b ). In northern Queensland, trees grew to a large size less than 100 m from the shoreline. In southern Queensland, however, it is recommended that lychee trees should not be irrigated with water having an electrical conductivity greater than 0.5 ms cm-1 (equivalent to about 340 mg soluble salts l - 1 ) ( Menzel, 1984b ). Damage sometimes occurred during dry weather, especially after fertilization of young trees, and showed as marginal and tip necrosis of the older leaves.

Whiley and Saranah (1980) grew young lychee trees in sand culture irrigated with 6 or 12 mM NaC1. At both concentrations, older leaves were shed with each new flush of growth. 'Tai So' was more susceptible than 'Bengal', and this was reflected in a greater uptake of salts. The concentrations of Na

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and Cl in the leaves of 'Tai So' after 13 months in the control and 12 mM NaC1 treatments were 0.24 and 22 mg Na g- 1, and 2.6 and 26.4 mg Cl g- 1, respectively.

Sodium chloride (1.6-2.3 kg per tree per year) was used in China as a fertilizer to improve fruit quality (i.e. sweeter fruit) (Anon., 1978). No information was available on the time of application or critical concentration required in the leaves or fruit to achieve better quality.

Critical experiments are warranted to determine what levels of NaC1 in the soil, water and leaf reduce lychee production. In other fruit trees, prolonged exposure to relatively low concentrations may reduce photosynthesis or yield before visible symptoms appear (Downton, 1977 ). A range of lychee cultivars needs to be tested for their tolerance to salinity. No information is available on a mechanism which imparts some degree of tolerance. The sensitivity of lychee to NaC1 via the leaf warrants examination if overhead irrigation is to be used in orchards. The technique of applying salt to improve fruit quality suggests that mild water stress prior to fruit harvest may have beneficial effects on fruit quality.

MYCORRHIZA

Coville (cited in Groff, 1921 ) was the first to show a mycorrhizal association in lychee. Mycorrhizal fungi were isolated from root tubercles of seedlings (from mountain lychees) grown in peat and sand. No such tubercles were found on seedlings grown in the standard mix of loam, sand and manure. Seedlings with the tubercles were larger and had a highly developed root system compared to those without the fungi. Similarly, Kadman and Slot (1974) showed that 'Tai So' seedlings were larger when grown in peat plus mycorrhizal ( ? ) soil compared to peat plus regular soil. No mycorrhiza were isolated from the soil or the seedlings.

The taxonomy, morphology and mycotrophic habit of the mycorrhiza associated with lychee were described by Pandey and Misra (1971, 1975). Rhizo- phagus litchi belongs to the vesicular-arbuscular group of phytomycetous endophytes. The endophyte could not be cultured on artificial media, the pres- ence of living roots being necessary for its survival. Mycorrhiza were only found on short-lived sublateral roots. Root penetration was through the epidermal cells into the cortex. Root hairs, the endodermis and vascular tissue were free of infection.

Since the earlier work of Coville, many authors have suggested that lychee requires mycorrhiza to grow satisfactorily (Katyal and Chugh, 1961, in India; Anon., 1978, in China), although healthy plants have been examined which were completely devoid of mycorrhizal tubercles ( Cobin, 1954). In India, it is suggested that new plants should be grown in soil taken from the vicinity of old trees to introduce the mycorrhiza (Chadha, 1968), while in China it has been suggested that the fungi grow better in acid compared to alkaline soils

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(Anon., 1978). High N and low K fertilization were reported to increase mycorrhizal growth in 'Rose Scented' in India (Rana and Srivastava, 1984).

It is well documented that mycorrhizal fungi are important in the uptake and transfer of soil nutrients ( especially P ) to many vascular plants (Peterson et al., 1984 ), but a critical role in lychee has not been firmly established. Pan- dey and Misra (1975) showed that infection with R h i z o p h a g u s l i tchi increased uptake of P and K into the shoot and increased root weight, t runk diameter and fruit yield of lychee in India (cultivar and age of trees not specified). It is possible that the greater growth recorded by Coville (cited by Groff, 1921 ) and Kadman and Slor (1974) was due to improved fertility or better pH of the mycorrhizal media. Similar media ( +_ pasteurization) need to be utilized before we can conclude a beneficial effect to the mycorrhiza.

FERTILIZER PRACTICES IN LYCHEE ORCHARDS

Y o u n g trees. - - The aim of early management is to obtain the greatest tree size and bearing surface. This is achieved by regular application of nutrients and water and appropriate pruning. The fertilizer program for young trees begins when the plants begin to flush (Table I ). The rate of each nutrient is increased each year. Fertilizer application is usually followed by irrigation unless heavy rain falls within a day of application. On poor soils, application of organic fertilizers can be used to great advantage in the first few years ( Cull and Pax- ton, 1983). Fertilizer should not be placed within 20 cm of the trunk, as the lychee is sensitive to fertilizer burn ( Koen and Smart, 1983a). Cull and Paxton (1983) also recommended that fertilizer application in subtropical Queens- land should be restricted to spring and early summer if there is a risk of frost, so that the plants are not flushing when winter approaches.

In the spring of Year 4, if trees are well-grown and flushing vigorously, N fertilizing should be stopped until leaf colour falls and/or fruiting begins ( Cull and Paxton, 1983 ). The application of fertilizers at this time should be supported by soil and leaf analysis. If this approach is not adopted, trees may not begin to bear regularly for several years. A well-grown 4-year-old tree can be 2.5 m high with a crown diameter of 3.0 m (Hams, 1985 ).

Bear ing trees. - - Table II shows that the timing of fertilizer application, total and relative amount of each nutrient varies greatly in different lychee orchards. Variations in the amount of each nutrient probably reflect variations in climate, soil type, cultivar, tree size and vigour, and possibly lack of knowledge of required levels. High rates of nitrogen are common in China and India (Nijjar, 1972; Chapman, 1984a).

The importance of controlling growth flushes with strategic application of N is well recognised in China as a means of determining the level and time of flowering (Chapman, 1984a). Early-maturing cultivars may flush 4 times per

TABLE I

Fertilizer practices for young lychee trees. No reliable information on and Taiwan

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fertilizer rates are available from China

Country Tree Amounts ofnutrients(g pertreeper age year) ~ (years)

N P K

Timing of fertilizer application (northern hemisphere equivalent )

Reference

Florida, U.S.A.

Hawaii, U.S.A.

India

South Africa

Australia

1 10 15 15 Monthly 2 14 20 20 3 28 40 40 l February, May, 4 56 80 80 August 5 112 160 160

1 34 34 34 2 68 66 68 3 136 136 136 4 272-410 272-410 272-410

Cobin (1954)

4-monthly Yee (1972)

1-3 175-350 20-60 105-235 ~ December, Nijjar (1981)

4-6 650-1200 75-125 300-470 J February, April

1 56 25 25 1 September - April (8 appl. ) Koen and Smart

2-3 140 25 50 September-April (5 (1983a)

4-5 280 25 100 appl. )

1 60 12 100 July, November, Hams (1985) 2 90 18 150 March 3 150 30 220 4 180 60 300

1 190 10 25 ~ N monthly; P, K Menzel et al. 2 350 40 100 f tri-monthly; organic (1986c) 3 530 70 150 in March in Years 2 4 390 10 50 and 3

JAssumes FYM contains 10 g N, 8 g P and 4 g K kg- ~ (A.P. George and R.J. Nissen, unpublished data, 1975).

year. Trees initiate floral buds on either the first or second flush produced after harvest provided the second flush does not occur after mid-October. The time of flushing is critical, since it determines the time of flowering in spring. Early flowering during cold damp weather may reduce fruit set. The timing of N application after harvest varies with cultivar (Winks et al., 1983 ). With proper nutrition, buds emerge by early October. Usually, no fertilizer is applied during autumn and winter in China so as to restrict growth flushing (Table II). This practice is more or less universal in other countries also ( Menzel, 1983; Menzel and Simpson, 1986a). Under a low plane of N, autumn growth will still occur with favourable weather, but will be less vigorous (Young, 1954).

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TABLE II

Fertilizer practices for N, P and K in lychee orchards. Amounts presented are for well-grown 10-year-old trees (100 kg crop)

Country Amounts of nutrients (g per tree per Timing of fertilizer Reference year) ~ application

(northern N P K hemisphere

equivalent) 2

Florida, 435-653 588-882 460-690 March, May, July Cobin (1954) U.S.A.

Hawaii, 763 327 633 December Yee (1972), H.Y. U.S.A. Nakasone (personal

communication, 1985)

India 1580 221 300 December, February Nijjar (1972) 1470 680 540 December, Nijjar (1981), A.S.

February, April Dhatt (personal communication, 1985)

South Africa 700 54 250 February, July

Taiwan

Australia

270 90 450 February, July 500 400 200 January, March

450 218 458 January, April, June

585 245 730 March, October 600 160 440 June, July

600 200 600 May, July 374 68 578 July

600 160 440 March, July

Langenegger (1974), Koen and Smart (1983a) Billett (1984) Gittens (1985)

Anon. (1981)

Loebel (1976) Cull and Paxton (1983) Menzel (1984b) Hams (1985), E.C. Winston (personal communication, 1985 ) D.J. Batten (personal communication, 1985 )

China 365-730 0 182-360 March, July Chen (1949) 800 640 320 January, March, Anon. (1978)

June 434-730 209-409 100-200 March, June Chapman (1984a)

1650 225 320 July 1610 180 800 March, June 1820 980 1400 February, April, Kay-ruing Chau

July (personal communication, 1985)

Hong Kong 615 442 486 January, July C.W. Fong (personal communication, 1985)

~Assumes FYM contains 10 g N, 8 g P and 4 g K kg- i; night soil contains 8.1 g N and 4 g K kg-1; pond mud contains 0.5 g N and 0.2 g K kg i. (A.P. George and R.J. Nissen, unpublished data, 1975). 2Floral initiation in January; fruit set in March; harvest in June-July.

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With the possible exception of South Africa and some regions of China (Table II ), the second time of fertilizer application is from 2 to 8 weeks prior to harvest to fill the fruit and improve eating quality. The timing of fertilizer application should be based on fruit development stage and relative nutrient accumulation rather than on calendar date. The benefits of very late application in lychee are questionable. Maximum fruit growth commences about 8-10 weeks after fruit set ( about 8 weeks before harvest).

There seems to be some confusion, both inside and outside China, on fertilizing around flowering. In China, trees may receive a boost (either by side dressing or by foliar spray) just prior flowering to strengthen the inflorescence and reduce fruit drop, but it is by no means universal ( see Table II). In South Africa, half the amount of N and K is applied at flowering (Koen and Smart, 1983a). Paxton and Chapman (1980) recommended that trees in subtropical Queensland should not be fertilized during spring, because it promoted growth flushes, and premature flower and fruit abscission, especially in early cultivars in dry weather. This is only a problem, however, when not all branches have set panicles. It is not known whether flushing in one branch can reduce fruit set and growth in an adjacent branch.

The question of fertilizing lychee trees around flowering time needs investigation. It is possible that the responses recorded in China reflect the generally lower plane of nutrition of the trees compared to other countries. The decision whether to fertilize or not should be supported by leaf analysis.

LEAF AND SOIL ANALYSIS

The rates of nutrients for lychee trees presented in Table II are only a guide, and nutrition management should be supported by leaf and soil analysis. Anal- ysis provides a guide to the balance of elements, including trace elements.

Tentative leaf standards for lychee have been developed in South Africa and Australia (Table III). Although no soil standards are available for lychee, values for other crops can be used as a guide (Table IV). Soil analysis may be undertaken in Hawaii prior to planting (H.Y. Nakasone, personal communication, 1985). Leaf analysis is sometimes performed in Florida (Cull, 1977) and India (D.J. Batten, personal communication, 1985 ) when deficiencies are suspected. They have been used to a very limited degree in Australia, but not in China or Hong Kong (D.J. Batten, L.S. Lee, E.C. Winston, Kay-ming Chau and C.W. Fong, personal communication, 1985 ). The leaf standards developed for lychee are within the range common to temperate and tropical fruit and nut trees (Table III), with the possible exception of N, P, K and Ca, which are at the low end of the range.

A standard time and tissue type has not been developed for lychee leaf analysis. In South Africa ( Lat. S ), the time of sampling is 6-8 weeks after fruit set (October-November) (Koen and Smart, 1983b). Leaves are sampled from

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TABLE III

Leaf nutrient standards for lychee. Values for deciduous and tropical fruit and nut crops also presented

Lychee, S. Lychee, Deciduous 1 and tropical 2 Africa (Cull, Australia fruit and nuts (Shear 1977 ) (Anon., 1983 ) and Faust, 1980; Anon.,

1983)

N (mgg 1) 13.0-14.0 13.0-14.0 10-35 P (mgg -1) 0.8- 1.0 1.7- 2.0 0.8-4.0 K (mg g- 1 ) 10.0 8.0-12.0 7 -35 Ca (mg g- 1) 15.0-25.0 5.6 6-60 Mg (mgg -1) 4.0- 7.0 2.1 2-40 C1 (mgg -1) ~ < 2.5 1.1-7.0

Na (#g g- 1 ) ? < 200 150-270 Mn (/~g g- 1) 50-200 30-500 0.3-3100 Fe (#g g- ~) 50-200 50-200 20-800 Zn (/~gg 1) 15 30-150 12-300 B (/~g g- 1) 27- 75 50-100 10-450 Cu (#gg-l) 10 5- 15 4-20

1Almond, apple, apricot, cherry, chestnut, filbert, peach, pear, pecan, plum, tung and walnut. 2Avocado, citrus, custard apple, guava, mango and persimmon.

the second compound leaf under the fruiting cluster. The two central leaflets from the leaf are selected. In Florida (Lat. N) , leaves are taken from non- flowering or non-flushing terminals during mid-flowering (March) (Young and Koo, 1964), while in India (Lat. N) leaves are sampled from dormant branches 2-3 months prior to floral initiation in December ( Nijjar, 1981 ). In Australia (Lat. S) , the most recently matured leaf is sampled between Sep- tember and January (Anon., 1983 ). The exact timing, or whether leaves should be sampled from flowering, flushing or dormant shoots, is not specified. Recent information from subtropical Queensland suggests that the mature leaf behind the fruiting cluster sampled in October, prior to fertilization in November, is the most reliable method ( C.M. Menzel, Carseldine and D.R. Simpson, unpublished data, 1986). These authors found that the levels of N, P, K, Zn and Fe were lower in fruiting compared to non-fruiting branches, while the opposite was true for Ca, Mg, Mn and B. The concentration of Cu did not show any consistent trend. The greatest response during the season was observed with K. Levels of this nutr ient in fruiting branches declined steadily from flowering to fruit maturi ty (the concentration of K in non-fruiting branches remained steady during the season). Under these circumstances, the choice of fruiting or non-fruiting wood and time of year altered the interpretat ion of leaf analysis for K.

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TABLE IV

Soil nutrient standards for tree, nut, vine and fruit crops suitable for assessment of lychee soils. Data from Anon. (1984b), except pH ( Nanz, 1955 ), B (Kabata-Pendias and Pendias, 1984) and Al (Ragland and Coleman, 1959)

Standard values for tree, nut, vine and fruit crops

Low No action required High pH < 5.0 5.0-5.5 > 5.5

Low Medium High Organic C ( % ) < 1.0 1-3 > 3.0 NO3-N ( mg kg- ~ ) < 20 20-40 > 40 P (mgkg 1) <20 20-60 >60 K (mg kg -~) <78 78-195 > 195 Ca (rag kg- ~ ) < 1 2 0 0 1200-1200 > 2000 Mg (mg kg- 1 ) < 192 192-384 > 384

No action required CI (rag kg - i ) < 250 Electrical conductivity (ms cm- ~ ) < 0.4 Na ( mg kg- ~ ) < 390 Cu (mg kg- I ) 0.3-10.0 Zn (mg kg -I) 2-15 Mn (rag kg -~) 2-50 Fe (mgkg -~) 2-50 B (rag kg- i ) 1.0-5.0 Al (mg kg- ~ ) < 540

Koen and Smart (1983b,c) suggested that the first leaf sample should be accompanied by a soil sample ( depth not specified); thereafter a soil sample once every 3 years would be sufficient. Leaf and soil samples should represent a planting of no more than 3 ha (separate samples are recommended for each soil type ). Approximately 20 uniform trees that are well spread are selected for sampling.

Cull and Paxton {1983 ) concluded that soil and leaf analysis in subtropical Queensland should be supported by assessment of yield, vigour and leaf colour for each cultivar and block of trees. This would indicate the need to increase or decrease fertilizer rates.

A survey of lychee leaf levels in southern Queensland (Table V) showed the most samples had excess N. Sixty-five percent of samples had excess Na, while 30-50% of samples were deficient in K, Ca, Fe and Zn. These samples were taken from January to July or November to December. It is possible tha t leaf age may have interfered with this response. In other experiments ( Menzel et al., 1987), the levels of P, K and Zn decreased with leaf age, while those of Ca,

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TABLE V

Range of leaf nutrient levels in lychee orchards in subtropical Queensland. Sixty-three sets of samples (means of 5-8 trees) from several orchards ('Bengal', 'Tai So', 'Haak Yip' (Hei Ye) and 'Wai Chee' (Huai Zhi) ) collected between January and July or November and December. Tree age ranged from 5 to 8 years

Nutrient Extreme Most Percentage of samples range frequent level

Deficient Adequate Excessive

N (rag g- l ) 12.5-19.4 16.0-17.0 3.2 3.2 93.6 P (mg g- i) 1.0-2.9 1.5-2.5 1.6 79.3 19.1 K ( mg g- 1 ) 3.6-11.1 8.5-9.5 52.4 47.6 0.0 Ca (mg g- l) 3.7-14.6 5.0-5.5 31.8 68.2 0.0 Mg (mg g 1) 2.5-6.6 3.5-4.5 0.0 100 0.0 C1 (mgg 1) 0.4-2.3 0.5-1.0 0.0 100 0.0 Na (/~g g 1) 100-800 100-200 0.0 34.9 65.1 Mn (#g g- 1 ) 18-466 180-210 4.8 95.2 0.0 Fe (#g g 1) 31-229 50-100 30.2 68.2 1.6 Zn (#g g- 1 ) 1-31 15-20 41.3 58.7 0.0 B (#g g- 1 ) 11-50 25-30 22.2 77.8 0.0 Cu (#gg 1) 1-64 5-10 11.1 65.1 23.8 A1 (/~gg 1) 17-132 40-80 0.0 1001 0.0

1Critical concentration for toxicity in rice is 300 ~tg g-1 (Tanaka and Navasero, 1966). Critical concentration for toxicity in cotton is 200 #g g 1 (Soileau et al., 1969).

Mg, Na, C1, Mn, B and Fe increased with age. The responses of N and Cu were variable; when they were readily available they accumulated in old leaves.

In subtropical Queensland, half the soil samples from lychee orchards had a soil reaction below that normally considered optimum for lychee (Table VI). About 30-50% of samples were low in K, Ca, Mg, Zn and Cu, while most of the samples had very low B levels.

Leaf analysis determined the nutritional status of many crops provided sampling, sample preparation and analysis were standardized ( Bould et al., 1960; Bould, 1963, 1968; Andrew, 1968; Jones, 1972; Munter et al., 1984). It was best used in conjunction with soil analysis, visual symptoms and pot/field experimentation. Most of the interpretations of leaf analysis were based on critical ( leaf level giving 90% of maximum growth as determined in pot experiments) or standard ( sampled from high-producing orchards) values, or ranges in concentration giving the limits of deficiency (low, sufficient, or adequate, high, and excessive or toxic ). Crop stage, leaf position, cultivar and environment significantly affected the relationship between leaf concentration and plant response.

It is obvious that further work is required to define leaf norms for lychee and the best sampling technique (time of year and whether leaves should be selected from flowering, fruiting, flushing or dormant wood). Leaves sampled from

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TABLE VI

Range of soil nutrient levels in lychee orchards in subtropical Queensland. Seventeen sets of samples (0-15 cm, means of 3-5 trees ) from 5 orchards ('Bengal', 'Tai So', 'Haak Yip' and 'Wai Chee') collected in July or November. Tree age ranged from 5 to 8 years

Extreme range Most Percent of samples in each frequent level category

Low No action High pH 4.6-6.6 4.5-5.0 47.1 23.5 29.4

Low Medium High Organic C ( % ) 1.5-5.0 2.5-3.0 0.0 70.6 29.4 NO3-N (rag kg- ' ) 3.4-50 3.4-10 76.5 17.7 5.8 P (rag k g - ' ) 95-585 95-100 0.0 0.0 100.0 K (mg k g - ' ) 16-480 50-150 35.3 47.1 17.6 Ca (rag k g - ' ) 190-1742 200-400 52.9 47.1 0.0 Mg (mgkg - ' ) 36-856 36-100 52.9 23.5 23.6

Low No action Excessive Na (rag k g - ' ) 2-1012 5-20 0.0 94.1 5.9 C1 (rag kg- 1) 2-30 5-10 0.0 100.0 0.0 Electrical conductivity 0.03-0.28 0.03-0.10 0.0 100.0 0.0 (ms cm- 1 ) 0.6-12.4 0.6-1.0 35.3 58.8 5.9 Cu (mg kg- 1 ) 1.3-14.1 1.3-2.0 29.4 60.6 0.0 Zn (rag kg- 1) 2-70 2-10 0.0 94.1 5.9 Mn (mg kg- ' ) 48-245 100-200 0.0 100.0 0.0 Fe (mg k g - ' ) 0.1-0.9 0.1-0.5 85.7 14.3 0.0 B (rag kg- 1 ) 14-629 100-200 0.0 85.7 14.3 Al ( nag kg - ' )

f r u i t i n g w o o d j u s t a f t e r f r u i t s e t m a y p r o v i d e t h e m o s t r e l i a b l e i n d i c a t i o n o f

t r e e f e r t i l i t y a n d a p p r o p r i a t e f e r t i l i z e r r a t e s . A s e t o f so i l n o r m s a l so n e e d s to

be e s t a b l i s h e d .

YIELD AND NUTRIENT CONTENT

The relationship between yield and nutrient content has been reviewed for a number of crops (Childers, 1966; Van Den Driessche, 1974), but similar information for lychee is scarce. Roy et al. (1984) studied the correlation between lychee yield ('Bombai') and leaf N, P and K levels in India. Two trees from each of 12 orchards, one high- and one low-yielding, were selected for analysis over 2 years. Yield was related ( r = 0.41-0.43, P < 0.05 ) to leaf N at flowering and at harvest and to leaf K at harvest. Yield was also correlated ( r-- 0.44, P < 0.05 ) with available soil K ( sampling time and depth not specified). There was no association between yield and P supply. Leaf and fruit

208

pests and diseases may have interfered with the response (yield losses of 25% or more because of fruit fly damage were common). Maximum leaf N levels (11.5 mg N g-1) were well below the level commonly believed to be opt imum under South African and Queensland conditions ( Table III).

Zhuang et al. (1983) showed that poor fruit set in Sovey Tung (known as Yuan Zhi in China) lychee was associated with low levels of NO3-N ( < 960/zg g - l ) , p ( <0.5 mg g- l ) and K ( <11.6 mg g- l ) in the leaf prior to and after fruit set. Levels of all nutrients fell after fruit set. Application of 3 g KH2 POt l - 1 during flowering reduced the rate of fruit drop.

Kobayashi and McLean (1985) related lychee yield (cultivar and age of trees unspecified) in Hawaii to leaf and soil nutrient levels. Fruit production was positively correlated with soil pH (range 5.4-5.1 ) and leaf N (maximum of 13.5 mg g - l ) and leaf Zn levels (maximum of 28/lg g - l ) . Yield was also correlated with July rainfall (just prior to harvest) and total rainfall between January and April (during panicle development) over 4 years. Fruit production was inversely related to the minimum temperature in July over 6 years. The physiological basis of these environmental effects were not discussed. The maximum leaf N levels are close to those considered opt imum for lychee in South Africa and Australia. The maximum level of Zn is very low.

REMOVAL OF CROP NUTRIENTS

There have been few investigations on the amount of nutrients removed by a lychee crop. Using the compositional tables provided by Singh (1952), Beyers et al. (1979) and C.M. Menzel, M.L. Carseldine and D.R. Simpson (unpublished data, 1986), a 100-kg crop ('Late Large Red', 'Bengal' and 'Tai So') would remove about 90-250 g N, 35-50 g P, 240-320 g K, 20-60 g Ca, 2.0-2.5 g C1, 1.0-1.4 g Na, 0.6-1.3 g Fe, 0.4-0.7 g Mn, 0.7-1.0 g Zn, 0.5-1.0 g Cu and 0.3-0.7 g B. Not considered in this analysis is the loss of nutrients in the panicle, flowers and aborted fruit ( Guardiola et al., 1984 ). Singh (1952) also showed that 40-50% of N, P, K and Cl were in the flesh ( 77.3% of fruit fresh weight), while 50-60% of Ca and Mg were in the skin ( 7.7% of fruit fresh weight). The seed (15% of fruit fresh weight) was a small source of most nutrients (7-25% of total) with the exception of N, which accounted for 37% of the total N in the fruit. His results suggest that N-accumulation in the fruit may be altered by seed size. The proportion of seed in lychee fruit varies greatly with cultivar, temperature, water supply and tree nutrition, and ranges from 5 to 30%.

Although limited investigations have been carried out on the nutrient composition of lychee fruit at maturity, only limited information is available during earlier stages of development. C.M. Menzel, M.L. Carseldine and D.R. Simpson (unpublished data, 1986) showed that the uptake of most nutrients was slow for the first 4-6 weeks after fruit set during skin development and was accelerated at about 7-8 weeks after fruit set during maximum aril growth.

209

These results are in contrast to those of Diver and Smith (1984), who showed that content of N, P, K and Zn in pecan nuts increased slowly until the tenth week after full bloom {beginning of endosperm growth), and then rapidly until nut maturity. Accumulation of Ca, Mg and Mn was linear throughout fruit development, while Fe increased rapidly during early kernel development, and then decreased as the nut matured.

ROLE OF NITROGEN

Numerous workers have investigated the role of nitrogen on lychee physiology: symptoms of deficiency; ecological studies on fertilizer practices and lychee performance: critical studies on the effects of time and rate of application at different stages of growth; relationship between leaf N and flushing patterns; and role of N on cold tolerance.

Symptoms of N deficiency in lychee include the following: general stunting of growth; uniform chlorosis of old leaves; curling of leaf margins; increased leaf inclination and texture; decreased leaflet size; chloroplast disorganization; failure of leaf development; defoliation; poor branching, flowering, fruit set and fruit retention; production of undeveloped fruit ( Goldweber, 1959; Mallik and Singh, 1965; Anon., 1967; Nijjar, 1973).

Young (1956, 1957) and Young and Harkness (1961) studied the performance of'Brewster' {known as Chen zi in China) lychees in Florida in relation to nitrogen nutrition over several years. Source (inorganic/organic), rate (0-200 g N per tree) and time {throughout the year) of N application varied from orchard to orchard. Groves also varied in tree age (4-14 years), climate, soil type and N content (4-110 mg NO3-N kg-1). Source, rate and time of N application and soil type had little or no observable influence on vegetativ- e/fruiting behaviour. Light bloom/yields were just as common in the relatively heavily fertilized orchards as in the groves where little or no fertilizer was used. At Davie, for example, trees were highly vegetative during autumn despite no fertilizer. In contrast, at Osprey, trees were fertilized heavily in July, Novem- ber and January, but bloomed and fruited heavily. There was a tendency, however, for heavy N application prior to the normal period of floral initiation (January) to reduce flowering when soil moisture and temperatures were favourable for growth. In addition, tree growth was larger and yields lower under high soil-N because the trees were prone to remain vegetative. No leaf N levels were presented. These authors concluded that other factors, such as temperature and soil moisture, exerted a greater control on the pattern of development (see Young, 1970).

Lynch {1954) and Young (1954) discussed the possible benefits of timing fertilization in lychee in Florida to apply no N after late summer until the time of floral initiation. A few years later, Nakata (1956) showed experimentally that late application of N (August/September vs. August) in Hawaii induced

210

flushing and reduced flowering (6.7 vs. 52.6%) and yield (0.4 vs. 7.9 kg per tree) in 'Brewster'. There were no differences in flowering or yield between trees fertilized in May or July. Both groups of trees flushed in October after heavy rain. In China, the timing of the autumn flush can be achieved by appropriate application of N ( Winks et al., 1983 ). If flushing occurs too early, fruit may set during cold weather. If flushing occurs too close to the normal period of floral differentiation (December), few panicles are initiated.

Young (1958), Young and Noonan (1959) and Youngand Koo (1964) studied the effects of nitrogen rate (32.0, 47.6 and 63.6 g N per tree) and source (NAN03, NH4N03, (NH4)2 S04 and organic N) on vegetative growth of 2- year-old 'Brewster' lychees in Florida. Trees averaged slightly less flowering and fruiting with organic N at the lowest rate. Leaf N levels (from non-flowering/non-flushing terminals at mid-flowering) varied from 17.8 to 23.5 mg g- 1. They concluded that the lower rates of fertilization were ample for young trees.

Tomer and Kadman (1985) noted that vegetative growth of 3 lychee cultivars ('Tai So', 'Bengal' and 'Brewster') was reduced by increased N supply (25-100 mg l-1) via the irrigation system in Israel. It is possible that continued supply of N may have interfered with Mg uptake (Joiner and Dickey, 1961 ). No leaf analysis was undertaken.

Koen et al. (1981a) investigated the effects of N on yield of 'Tai So' lychee over 8 years in South Africa. The highest N level (140 increasing to 1000 g per tree per year, applied at flowering and harvest) gave the highest yield. In other experiments (Langenegger, 1975; Koen et al., 1981b; Koen and Smart, 1982), very high rates of N depressed yield, presumably because of excessive vegetative flushing. There was a strong correlation between yield and leaf N up to 14.7 mg N g- 1.

In India, fertilizer N ( 250-1000 g per tree per year) increased fruit set, fruit retention and yield compared to unfertilized control trees (12-year-old 'Seed- less Number One') (Yamdagani et al., 1980). No soil or leaf N levels were determined, nor were the times of N application specified. In South Africa and India, N fertilization at flowering increased fruit size, sugar/acid ratio and reduced the proportion of malformed fruits (Langenegger, 1975; Koen, 1977; Koen et al., 1981a,b; Bose et al., 1986).

Several crops have shown an increase in fruit set after N fertilization (e.g. apple (Williams, 1965 ) and guava ( Mansour et al., 1981 ) ). In apple, the effect of late summer N was to increase ovule longevity and hence prolong the effec- tive pollination period.

In China, 2-3 g N l- 1 as urea, sprayed before and/or after fruit set, reduced fruit drop and increased yield in lychee (Batten, 1983; Winks et al., 1983; Chapman, 1984a). Similar trials in Australia have shown no response, possibly because the trees were managed at a higher level of nutrition. Levels of N in the leaves before and after spraying were not determined in these experiments.

211

In northern Thailand, floral initiation in 'Tai So' achieved by water stress and cincturing was associated with a C/N ratio in the leaves of 1.75 ( Chapman, 1984a). In contrast, similar treatments in Hawaii with the same cultivar did not alter carbohydrate levels (Nakata and Suehisa, 1969). Fruitfulness in other crops was associated with a particular C/N ratio, with the ideal ratio varying for floral initiation and fruit set (Kraus and Kraybill, 1918; Chaplin and West- wood, 1980). Recently, however, the whole question of C/N ratio has come under question. For some crops, such as avocado, floral initiation in winter was preceded by a period of low carbohydrate levels (Scholefield et al., 1985; but see Bodson, 1977). Menzel and Paxton (1986) suggested that floral initiation in lychee was controlled by a balance of endogenous growth substances which altered the distribution of plant dry matter in favour of vegetative or reproductive growth.

Nitrogen is the only nutrient which has a direct effect on floral initiation in plants. High N reduced flowering while low N promoted flowering in tissue culture (El Hinnawy, 1956; Wada and Shinozaki, 1985). Phosphorus and K had no significant effect. The addition of sucrose to the media often accelerated or increased the level of flowering, suggesting an interaction between C and N (Wada and Totsuka, 1982; Friend et al., 1984). Similar experiments are required in lychee.

Menzel et al. (1986a) investigated the seasonal pattern of flushing and leaf N levels in 8-year-old 'Tai So' lychees in subtropical Queensland. Trees flushed after harvest (January) in response to N application. This flushing continued into May and June at the heaviest application (1600 g N per tree per year). Leaf N levels rose after fertilization in November and January, declined slowly during flushing, vegetative dormancy and flowering, and then more rapidly after fruit set. The greatest decline was in trees given 100 g N per year (leaf N fell to 10.2 mg g- i ).

Young and Noonan (1958) noted great differences in cold (0 to -4°C) damage among 'Brewster' trees in Florida receiving N from different sources, which could not be readily explained by differences in flushing pattern. The degree of cold-tolerance increased in proportion of NH4:N03 available to the tree. Sixty-five percent of 1-year-old trees fertilized with NaNO3 died compared to 25-30% of those trees receiving N from other sources ((NH4) 2SO2,NH4 NO3, sludge or combinations). Rate of application had no observable effect on freeze damage.

Only limited information seems to be available linking crop development in lychee to leaf N levels. It is difficult to determine visually when N excess commences (Mills and Jones, 1979). Most fruit plants continue to grow vigorously, exhibiting a deep dark green colour. Vegetative growth is often stimulated at the expense of flower or fruit set. The level of leaf N that is excess for pro- ductivity has been well defined for a number of crops, e.g. 22 mg g- 1 in apple (Boynton and Oberly, 1966) and 16-20 mg g-1 in avocado (Embleton and

212

Jones, 1966). It is not known what critical N level is required to prevent winter flushing or to encourage successful fruit set and development in spring. Pre- sumably, higher leaf levels are needed for successful reproductive development.

The modelling of N in plants and the development of minimum { no growth) and maximum N concentrations in tissues has been a useful technique for predicting responses to applied N in several crops and may have potential in lychee (Greenwood, 1977; Angus and Moncur, 1985).

ROLE OF PHOSPHORUS

Symptoms of P deficiency in lychee are tip and marginal necrosis (coppery- brown colour) of mature leaves proceeding towards the midrib (Goldweber, 1959; Mallik and Singh, 1965). Under severe deficiency, leaves curl, dessicate and abscise prematurely. Phosphorus deficiency may occur in soils well sup- plied with P because of reduced availability ( acid or alkaline soils), although some sandy/organic soils are naturally low in P (Maynard, 1979).

Young 'Brewster' and 'Purbi' marcots grown in sand culture under low or nil P closely resembled control plants ( Goldweber, 1959; Mallik and Singh, 1965). Shoot and root growth proceeded normally, except for increase in trunk girth and premature leaf drop. Goldweber (1959) also noted that all - P plants flowered and set fruit, although fruit were smaller than the control plants. Mallik and Singh's (1965) data show no close relationship between leaf P levels and P supply to the roots; P levels at the end of the experiment when deficiency symptoms were visible for control, 2P and 1/8 P treatments were 1.1, 5.1 and 3.1 mg g-l , respectively. This suggests that leaves other than the recently matured leaf were used for analysis. Levels above 0.8-2.0 mg P g- 1 are considered adequate in lychee (Table I). Increasing the amount of P to the plants reduced the levels of N and K.

Only slight responses to fertilizer P have been recorded in lychee (Koen, 1977; Koen et al., 1981a; Koen and Smart, 1982). For instance, Koen et al. (1981a) studied the effect of variable levels of P ( 0, 300 and 600 increasing to 0, 750 and 1500 g per tree over 8 years) in 9-12-year-old 'Tai So' trees in South Africa. Average yields from 3 seasons (1976, 1978 and 1979) were 37.8, 42.3 and 45.8 kg per tree, respectively. No explanation was given for the absence of fruiting during the other seasons. Fruit quality was not affected by P supply. Soil (resin extract) and leaf P levels ranged from 2.7 to 8.9 mg kg-1 and from 1.2 to 1.8 mg g-1, respectively. A reaction to P was not expected unless soil levels were less than 6 mg kg-1 (resin extract).

Recent information from Thailand (Chapman, 1984a) suggests that heavy applications of P as superphosphate (up to 900 g P per tree) may substitute for cincturing. No information was provided on the possible mechanism (did it induce deficiencies of other nutrients? ), timing of application or long-term effects on tree health. It is possible that the promotion of flowering by P was

213

due to a reduction in the uptake of soil N because of N-P interactions (Chua and Chuo, 1981 ).

Although fruit trees deficient in P showed fewer vegetative and floral buds and delayed fruit set (Taylor and Goubran, 1975; Reddy and Majmudar, 1983 ), no increases in yield after P application to trees adequate in P have been reported ( Chaplin and Westwood, 1980). Recent studies in mango ( Reddy and Majmudar, 1985 ), however, have shown a strong relationship between P content in shoots and the level and timing of panicle initiation and development. Further studies are required before we can account for a role of P in lychee fruit set and growth.

ROLE OF POTASSIUM

The first symptom of K deficiency in lychee was a loss of leaf colour (Gold- weber, 1959). Necrotic areas then developed in leaf apices, which gradually progressed along the margins towards the base. Mature leaves abscised prematurely. Consequently, the canopy consisted of small terminal clusters of leaves. Plants flowered, but did not set fruit. Severe deficiency in solution culture reduced plant height, trunk girth and root development and caused tree death (Goldweber, 1959; Mallik and Singh, 1965). These responses were not associated with reduced leaf levels (11.5-12.6 mg K g - l ) , possibly because physiologically young leaves were used for analysis. Potassium deficiency was also induced by Mallik and Singh (1965) when plants were given extra N (leaf levels of 15.3 mg K g- l ) .

Potassium deficiency is common on acid, highly-leached sandy soils, on cer- tain organic soils and on soils where K is fixed in a non-exchangeable form (Maynard, 1979). Deficiency of K can often occur late in the season when K is translocated to developing fruit.

Joiner (1958, 1959) and Joiner and Dickey (1961) grew 'Brewster' marcots in sand under variable K levels (8, 32 and 180 mg K l-1 in nutrient solution applied 4 times daily). Potassium increased leaf K levels (10.7-24.3 mg g- i ) , but reduced shoot extension and trunk growth, especially under high rates of N. This was associated with reduced Mg content in the roots. Magnesium levels were negligible (0.1 mg g-1) under high K and N supply.

No responses to fertilizer K have been reported i~ lychee ( Koen, 1977; Koen et al., 1981a; Koen and Smart, 1982 ). Rates up to 500 g per tree per year (for 9-12-year-old 'Tai So') were used in South Africa. Soil and leafK levels ranged from 50 to 61 mg kg -1 and from 9.1 to 10.6 mg g-i , respectively. No response was expected unless soil levels were below 56 mg K kg- 1.

Application of K increased vegetative and reproductive growth in fruit trees deficient in K ( Chaplin and Westwood, 1980). In contrast, no response in fruit set has been observed in trees considered adequate in K for vegetative growth ( Vang-Petersen, 1975).

214

Banta (1952) suggested that K application to lychee in autumn was useful in Florida because it helped to reduce excessive vegetative growth. Limited information from subtropical Queensland indicates that K may reduce winter flushing and improve flowering (Menzel and Simpson, 1986b). Seven-year- old 'Tai So' trees were given no fertilizer, standard fertilizer ( 270 g of N and K per tree per year split between November and January) or high K fertilizer (100 g N and 145 g K per tree per year split between November and January plus 375 g K applied in February). The amounts of flowering in the terminal branches in late winter in these treatments were 12.0, 26.0 and 94.0%, respectively. The level of flowering was related to leaf K activity. Leaf N levels were lower in flowering trees, presumably because of translocation to the developing panicle.

The possible beneficial effects of K on winter dormancy in lychee require further experimentation. The timing and rate of application and the ratio of N to K may be critical. Further work is also required on the role of K on fruit set and fruit development. Foliar sprays of K may boost tree health and improve fruit quality on trees considered adequate for K.

ROLE OF CALCIUM

Symptoms of Ca deficiency in lychee include: small leaflets; leaf necrosis along margins; severe leaf drop; poor root development (Goldweber, 1959). Deficient plants grown in solution culture flowered, but did not set fruit. No leaf levels were determined.

No responses to fertilizer Ca have been reported. Lychees grew and cropped in calcareous soils in India, California and Florida ( Cobin, 1954; Lynch, 1958; Nijjar, 1972; Campbell and Malo, 1975), provided attention was paid to Fe supply ( Malcolm, 1953 ). Even on low pH soils, it is exceptional to observe the classical symptoms of Ca deficiency in most crops, presumably because of the wide use of superphosphate, lime and gypsum ( Kirby and Pilbeam, 1984 ).

ROLE OF MAGNESIUM

Lychee plants with Mg deficiency displayed small leaves, interveinal necrosis, leaf abscission and poor root development (Goldweber, 1959). Under severe deficiency, flowering was suppressed. Dolomite instead of lime was recommended for the correction of Mg deficiency in sandy soils in coastal southern Queensland (Anon., 1984a).

Magnesium deficiency was induced in 'Brewster' marcots grown in sand culture under high rates of N and K (Joiner, 1958, 1959; Sites and Joiner, 1959). Magnesium levels in the roots declined from 1.3 to 0.1 mg Mg g-1. In other experiments (Joiner and Dickey, 1961 ), high Mg levels in the nutrient solution (54 compared to 12 mg Mg 1-1 ) increased t runk growth, especially at the

215

low level of substrate N. Magnesium levels in the roots and shoots were not determined.

The interaction between N, K and Mg requires further investigation under field conditions. Potassium-induced deficiency of Mg has been noted in other crops (Holmes, 1962). It could be a problem when young trees growing in sandy soils are given large doses of N and K to induce rapid vegetative growth.

ROLE OF MICRONUTRIENTS (Zn, B, Fe, Cu and Mn)

Limited descriptions are available for micronutrient deficiency symptoms in lychee. Symptoms of Zn deficiency include: general bronzing of leaflets; smaller leaflets; long internodes; smaller fruit with reduced flesh recovery and sugar content (Dutt, 1962; Nijjar, 1972; Awasthi et al., 1975; C.M. Menzel, unpublished data, 1985). Iron deficiency is characterised by general chlorosis of young leaves, spreading to older leaves ( Malcolm, 1953 ). Severe deficiency may cause branch die-back. Symptoms of B and Cu deficiency are small fruit with reduced pulp percentage (Dutt, 1962 ). No descriptions of Mn deficiency are described in the literature. D.J. Batten (personal communication, 1985) reported that Zn and Cu deficiency may sometimes occur together in lychee in Australia. Typical symptoms were small leaves, interveinal chlorosis/mottling and terminal die-back. A similar complex was noted by M.F. Piccone ( personal communication, 1985 ) in South Africa.

Boron deficiency is a serious world-wide problem and is common on acid sandy soils where native B has been leached and on alkaline soils with free lime, on acid organic soils and on sandy soils with a low organic matter content ( Maynard, 1979; Gupta, 1979). Iron deficiency is common on calcareous soils and over-limed soils because of reduced availability of native Fe and to a lesser extent on poorly drained acid soils ( Chen and Barak, 1982 ) and after excessive P fertilization ( Rediske and Biddulph, 1953). Soils with a pH greater than 6.8 and indiscriminate liming may induce Mn deficiency (Mesdag and Balkema- Boomstra, 1984). Zinc deficiency occurs on a variety of soil types because native Zn is low (acidic leached sands), unavailable to plants ( alkaline soils ) or com- plexed to soil components (organic soils) (Maynard, 1979). Deficiency is intensified by heavy N fertilization ( Ozanne, 1955 ). Copper deficiency is most likely in soils with inherently low Cu content (sandy textured soils, highly weathered ferrallitic and ferruginous soils), although Cu availability may be low because of complexing with organic matter (organic soils) or because of alkaline pH (calcareous soils) ( Maynard, 1979; Alloway and Tills, 1984 ). Rel- atively high concentrations of N, P and Zn in the soil can exacerbate the deficiency problem.

Boron appears to play a significant role in fruit set of many crops. Plants marginally deficient in B exhibited blossom wilting and necrosis, reduced pollen production and viability and poor fruit set, whereas vegetative growth was

216

unaffected (Hanson and Breen, 1985a). Boron applied to plum, sweet cherry and filbert trees not deficient in B resulted in a significant increase in fruit set and yield ( Chaplin and Westwood, 1980). The authors suggested that there is a demand for B which is unrelated to the general nutrition of the tree. In more recent experiments with plum ( Hanson and Breen, 1985a), the amount of fruit set was related to B levels in the flowers. Remobilization of B from leaves to the reproductive structures was limited when leaf levels were low. In addition, less than 15% of floral B was translocated to the bud prior to bud swelling (Hanson and Breen, 1985b). They suggested that remobilization of B in the xylem of branches prior to bloom was more limited than for any of the other nutrients.

Zinc deficiency leads to premature flower dehiscence and ovule abortion in a range of crops ( Khanduja et al., 1974; Bould et al., 1983 ). Copper deficiency can induce pollen sterility and hence limit fruit set in crops, although vegetative growth was normal (Alloway and Tills, 1984). There is also a report of Mn (Mac Swan cited in Chaplin and Westwood, 1980) increasing fruit set in other crops, but its role has not been firmly established.

The results of published investigations show that in most cases, application of micronutrients (Zn, B and Cu ), even when applied with growth regulators, had only a slight effect on fruit set, fruit abscission or fruit quality in lychee (Hoda et al., 1973; Hoda and Syamal, 1975; Awasthi et al., 1975; Pujari and Syamal, 1977; Verma et al., 1980; Sharma and Dhillon, 1984). There are only two reports ( Dutt, 1962; Xu et al., 1984) that they significantly improved fruiting. Dutt sprayed trees (age and cultivar unspecified) in India with 3.05 g Cu 1-1, 2.70 g Zn 1-1 or 0.18 g B 1-1 prior to flowering. The number of fruit per tree at harvest was 40, 200, 100 and 70 for the control, Cu, Zn and B spray, respectively. All fruit produced by the control trees ( 3 ) were immature. Those produced after B treatment (1 tree) were partially immature. All the fruit produced after Zn or Cu spray were large and sweet (1 tree each). No soil or leaf levels were determined. Xu et al. (1984) increased fruit yield in 15-20- year-old trees by 3-4 times after spraying with 0.45 g B l- 1 or applying 20-25 g B per tree ( ground coverage of trees about 15-20 m 2). No leaf or soil analysis was presented, nor were the times of application recorded. The actual yields per tree were not indicated.

Malcolm (1953) overcame Fe deficiency with a drench of 4 g Fe (as Fe- EDTA) in young 'Brewster' lychee trees (age unspecified) growing in calcareous soil in Florida. Leaf chlorosis disappeared within a few days in trees slightly affected, while 60 % of trees showing branch die-back recovered with new green growth after 8 weeks.

Micronutrient deficiencies were not a problem in lychee cultivation in China (Kay-ming Chau, personal communication, 1985) because of the general use of organic fertilizers (FYM, legumes, green manures and bean cakes).

Foliar sprays are recommended for the correction of micronutrient deficien-

217

cies in lychee at the following rates: 0.45-2.70 g Zn l-1 (ZnS04 7H20 or ZnO); 0.11-0.45 g B 1-1 (H3B03 or Na2B407); 0.51-3.05 g Cu 1-1 (CuS04 4H20); 0.59 g Mn 1-1 (MnS04 5H20); 0.48 g Fe 1-~ (FeS04 7H20) (Cobin, 1954; Saeed, 1961; Nijjar, 1972; Verma et al., 1980; Anon., 1978; D.J. Batten and Kay- ming Chau, personal communication, 1985 ). Frequency or time of application were usually not specified. Yearly application of B and Zn were recommended in New South Wales ( D.J. Batten, personal communication, 1985 ), while yearly application of Zn in spring after new leaves matured was recommended by Nijjar (1981) in India.

Deficiencies of Zn, B and Cu in subtropical Queensland can be overcome by single soil applications during summer every 2-3 years ( Menzel, 1984b ). Sug- gested rates for well-grown 5-year-old trees (ground cover of 4 m 2) were 22.7 g Zn, 0.9 g B and 2.0 g Cu. Similar rates of B were recommended for lychee in tropical Queensland (E.C. Winston, personal communication, 1985). Times of application were April and August.

Leaf symptoms of B, Cu and Mn deficiency should be described. The possible role of B, Cu, Zn and Mn on reproductive development needs clarification. Future work should record levels of these elements in the leaves before and after treatment. It is possible that water stress may have interfered with the response to these nutrients. No information is available on the relative merits of foliar or soil application in relieving deficiencies of the nutrients. There is some indication that soil fixation may be a problem with B and Zn application (D.J. Batten and E.C. Winston, personal communication, 1985 ).

A NUTRITION PROGRAM FOR LYCHEE

A tentative nutrition program for lychee is shown in Fig. 1. Fertilizer application should be supported by leaf and soil analysis, with a visual record of tree vigour, bloom and yield. Ultimate rates of application depend on tree vigour, crop load, cultivar, soil type and climate. The timing of fertilizer application and recording of tree response depend on stage of tree growth which varies with cultivar, orchard and year.

CONCLUSION

Low and irregular bearing of lychee can often be attributed to unfavourable weather conditions (Menzel, 1983, 1984a). However, even with a favourable climatic environment, a tree may not carry a single fruit at harvest. This is mainly due to excessive vegetative flushing in winter following late or heavy N fertilization. Deficiencies of N and K, and to a lesser extent of B, Cu and Zn, may limit yield by restricting the set and subsequent development of fruit. In a few cases, soil features (pH, salinity, drainage problems) may impair tree health and hence indirectly reduce fruit production.

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FRUIT MATURITY

VEGETATIVE FLORAL GROWTH INITIATION

DORMANCY

FRUIT SET

FLOWERING

J J A S O N D J F M A h4 J

J F M A M J J A S O N D J

adjust ~ N,P,K soil pH N,P~ K app l i ca t i on application (plus m i c r o n u t r i e n t s )

K app l i ca t ion ? N,K,B, Cu, Zn app l i ca t i on ?

Record Record Leaf and soil Record v igour bloom ana lys is yie[d

Fig. 1. A tentative nutrition program for lychee. The beneficial effects of K application in autumn and N, K, B, Cu and Zn application in spring need to be confirmed. Both northern and southern hemisphere equivalent seasons are presented.

The development of nutrition management to maintain tree health and encourage successful flowering and fruiting in lychee depends on improving our understanding of the role of each nutrient on the different components of growth. Priority research areas for nutrition management should include: def- inition of the relationship between leaf flushing patterns and leaf N levels; the timing of fertilizer N application during flowering and fruit set; examination of leaf sampling techniques; refinement of leaf nutrient standards; development of soil nutrient standards; possible beneficial effects of increased K supply on winter dormancy; leaf symptoms of micronutrient deficiencies; and possible roles of B, Cu and Zn on fruit set.

219

AC KNOWLEDGEMENTS

M.L. Carseldine, G.H. Price and G.E. Rayment contributed to Tables V and VI. Unpublished information from D.J. Batten, L.S. Lee, M.F. Piccone, E.C. Winston (Australia), Kay-ming Chau (Peoples Republic of China), C.W. Fong ( Hong Kong), A.S. Dhatt { India) and H.Y. Nakasone (Hawaii) is gratefully acknowledged. We thank Z. Singh (India) and A.J. Joubert (South Africa) for lychee reprints.

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Lychee nutrition: A review